In the last 30 days

• Open/close Direct patterning on reduced graphene oxide nanosheets using femtosecond laser pulses

  Zhi-Bo Liu et al 2011 J. Opt. 13 085601 Tag this article

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  Micro- and nanostructures were fabricated directly on graphene nanosheets by controlling the conditions of femtosecond laser pulse etching. High quality graphene micro- and nanostructures with a minimum width of 492 nm were obtained as the graphene nanosheets used in our experiments were large-scale, uniform and highly conductive. Various complex patterns were successfully created through femtosecond laser etching. Furthermore, by managing the laser energy, the graphene under the Au electrodes could be completely or partly removed. This technology of direct patterning of micro- and nanostructures on graphene through femtosecond laser technology might pave the way for the integration of graphene-based electronic microdevices.

• Open/close Spin-to-orbital conversion of the angular momentum of light and its classical and quantum applications

  Lorenzo Marrucci et al 2011 J. Opt. 13 064001 Tag this article

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  A few years ago the possibility of coupling and inter-converting the spin and orbital angular momentum (SAM and OAM) of paraxial light beams in inhomogeneous anisotropic media was demonstrated. An important case is provided by waveplates having a singular transverse pattern of the birefringent optical axis, with a topological singularity of charge q at the plate center, hence named ' q-plates'. The introduction of q-plates has given rise in recent years to a number of new results and to significant progress in the field of orbital angular momentum of light. Particularly promising are the quantum photonic applications, because the polarization control of OAM allows the transfer of quantum information from the SAM qubit space to an OAM subspace of a photon and vice versa. In this paper, we review the development of the q-plate idea and some of the most significant results that have originated from it, and we will briefly touch on many other related findings concerning the interaction of the SAM and OAM of light.

• Open/close Plasmonic light trapping in thin-film Si solar cells

  P Spinelli et al 2012 J. Opt. 14 024002 Tag this article

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  Plasmonic nanostructures have been recently investigated as a possible way to improve absorption of light in solar cells. The strong interaction of small metal nanostructures with light allows control over the propagation of light at the nanoscale and thus the design of ultrathin solar cells in which light is trapped in the active layer and efficiently absorbed. In this paper we review some of our recent work in the field of plasmonics for improved solar cells. We have investigated two possible ways of integrating metal nanoparticles in a solar cell. First, a layer of Ag nanoparticles that improves the standard antireflection coating used for crystalline and amorphous silicon solar cells has been designed and fabricated. Second, regular and random arrays of metal nanostructures have been designed to couple light in waveguide modes of thin semiconductor layers. Using a large-scale, relative inexpensive nano-imprint technique, we have designed a back-contact light trapping surface for a-Si:H solar cells which show enhanced efficiency over standard randomly textured cells.

• Open/close A spacetime cloak, or a history editor

  Martin W McCall et al 2011 J. Opt. 13 024003 Tag this article

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  We introduce a new type of electromagnetic cloak, the spacetime cloak (STC), which conceals events rather than objects. Non-emitting events occurring during a restricted period are never suspected by a distant observer. The cloak works by locally manipulating the speed of light of an initially uniform light distribution, whilst the light rays themselves always follow straight paths. Any 'perfect' spacetime cloak would necessarily rely upon the technology of electromagnetic metamaterials, which has already been shown to be capable of deforming light in ways hitherto unforeseen—to produce, for example, an electromagnetic object cloak. Nevertheless, we show how it is possible to use intensity-dependent refractive indices to construct an approximate STC, an implementation that would enable the distinct signature of successful event cloaking to be observed. Potential demonstrations include systems that apparently violate quantum statistics, 'interrupt-without-interrupt' computation on convergent data channels and the illusion of a Star Trek transporter.

• Open/close Known-plaintext attack-free double random phase-amplitude optical encryption: vulnerability to impulse function attack

  Pramod Kumar et al 2012 J. Opt. 14 045401 Tag this article

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  A security enhanced double random phase-amplitude encryption (DRPAE) scheme is immune against the powerful known-plaintext attack, due to the insertion of an undercover amplitude random mask at the Fourier plane in the conventional double random phase encryption (DRPE) scheme. However, DRPAE, which nullifies the high level known-plaintext attack, is found to be susceptible to a simple impulse function attack. Information about the exact distribution of the amplitude mask as well as that of the Fourier plane random phase mask is divulged from an impulse function attack. A variant form of the impulse function attack is also able to show that the DRPAE scheme is as linear as the conventional DRPE scheme. Numerical simulation results validate the effectiveness of the simple impulse attack on the DRPAE scheme.

• Open/close Toward high-efficiency solar upconversion with plasmonic nanostructures

  Ashwin C Atre et al 2012 J. Opt. 14 024008 Tag this article

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  Upconversion of sub-bandgap photons can increase the maximum efficiency of a single-junction solar cell from 30% to over 44%. However, upconverting materials often have small absorption cross-sections and poor radiative recombination efficiencies that limit their utility in solar applications. Here, we show that the efficiency of upconversion can be substantially enhanced with a suitably designed plasmonic nanostructure. The structure consists of a spherical nanocrescent composed of an upconverter-doped dielectric core and a crescent-shaped metallic shell. Using numerical techniques, we calculate a greater than 10-fold absorption enhancement for a broad range of sub-bandgap wavelengths throughout the entire upconverting core. Further, this nanocrescent enables a 100-fold increase in above-bandgap power emission toward the solar cell. Our results provide a framework for achieving low-power solar upconversion, potentially enabling a single-junction solar cell with an efficiency exceeding the Shockley–Queisser limit.

• Open/close Band-stop filters based on a coupled circular ring metal–insulator–metal resonator containing nonlinear material

  Gaige Zheng et al 2012 J. Opt. 14 055001 Tag this article

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  An all-optical plasmonic filter based on a metal–insulator–metal (MIM) waveguide coupled with a circular ring resonator containing a Kerr nonlinear medium is proposed and numerically investigated. The optical filtering effect is verified by the finite difference time-domain (FDTD) method and the simulation results reveal that the increase in the refractive index induced by enhancing the incident intensity can cause a red-shift for the resonance wavelengths. Thus the resonant wavelengths can be tuned without changing the outer size of the structure. The proposed band-stop plasmonic filter is of a compact size that has potential application for integrated optics in which we have limitations on the outer dimensions and it is not possible to enlarge the dimension of the ring resonator to reach longer resonant wavelengths.

• Open/close iTweezers: optical micromanipulation controlled by an Apple iPad

  R W Bowman et al 2011 J. Opt. 13 044002 Tag this article

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  The 3D interactive manipulation of multiple particles with holographic optical tweezers is often hampered by the control system. We use a multi-touch interface implemented on an Apple iPad to overcome many of the limitations of mouse-based control, and demonstrate an elegant and intuitive interface to multi-particle manipulation. This interface connects to the tweezers system hardware over a wireless network, allowing it to function as a remote monitor and control device.

• Open/close 3D photonic crystals for photon management in solar cells

  Ralf B Wehrspohn and Johannes Üpping 2012 J. Opt. 14 024003 Tag this article

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  Light management in single and multi-junction solar cells is becoming increasingly important to optimize the optical and electro-optical properties of solar cells. The limits of light path enhancements are discussed for non-resonant and resonant optical nanostructures as well as for angular-selective and energy-selective approaches. The potential of 3D photonic crystals for photon management in solar cells is discussed for the corresponding concepts and the state of the art is reviewed.

• Open/close Plasmon enhanced light amplification in metal–insulator–metal waveguides with gain

  Xiao-Lan Zhong and Zhi-Yuan Li 2012 J. Opt. 14 055002 Tag this article

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  In this paper we study the loss compensation and light amplification properties of metal–insulator–metal (MIM) waveguides that are doped with gain material in the dielectric core. An analytical approach based on Maxwell’s equations is developed to evaluate quantitatively the influence of the gain coefficient on the loss compensation and light amplification efficiencies of the waveguide under different values of the waveguide width and working wavelengths. The analytical results agree excellently with all-numerical calculations that directly solve Maxwell’s equations. The results show that the light amplification efficiency obeys a strict linear relationship with the gain coefficient, and MIM waveguides with narrower widths and under shorter wavelengths have better efficiencies. In addition, the MIM waveguides have higher light amplification efficiencies than usual dielectric waveguides, which suggests a very positive role of the plasmonic structure in enhancing the light amplification when gain is introduced. These loss and gain behaviors can be well explained by looking at the modal profile of each transport mode and the corresponding light energy confinement effect and slow light effect.